This invention relates to dot matrix type serial printers for printing characters of any number as desired in one line of characters of a predetermined length, and more particularly it is concerned with a dot matrix type serial printer of the type described which is capable of varying as desired the pitch of dots for forming each character in the direction in which the characters are to be printed in one line.
When printing data having a predetermined number of characters to be printed in one line is printed by means of a serial printer using a series of wires in a row for forming characters by dots in which the length of one line of characters is too short to accommodate the predetermined number of characters to be printed in one line of the printing data, it has until now been necessary to vary the pitch of the dots in the line of characters in accordance with the length of one line of characters and the number of characters to be printed in one line of the particular serial printer to be used.
Because of this, it has been the usual practice, in a serial printer of the prior art in which characters are printed in the form of a dot matrix by moving in reciprocatory movement a print head by means of a step motor or a DC motor along one line of characters to be printed, to provide pulse generating means, such as a rotary encoder, for detecting the position to which the print head moves. The pulse generating means is operative to output, as the print head moves, pulse signals in which each has a frequency divided by an integer in accordance with the length of one line of characters and the number of characters to be printed in one line of the particular serial printer, so as to produce timing signals which allow the pitch of the dots for printing characters to be adjusted to carry out dot printing satisfactorily.
In a serial printer of a timer type, it has been the usual practice to provide a timer circuit for producing timing signals, and to set the timer circuit at a predetermined time in accordance with the length of one line of characters and the number of characters to be printed in one line of the particular serial printer. After the timer circuit is started in timed relation to the commencement of the movement of the print head, a timing signal is generated by the timer circuit at each predetermined time, so as to print characters at a desired pitch of the dots in a direction in which the characters are to be printed in one line.
Some disadvantages are associated with the serial printers of the prior art noted hereinabove. The problem with which the serial printer of the type in which the frequency of each pulse signal is divided by an integer is that it is only by an integer that the frequency of each pulse signal is divided and it is impossible for this type of serial printer to print characters at various dot pitches obtained by dividing the frequency of each pulse signal by a number which is not an integer.
In the serial printer of the timer type, the timer circuit is started by a drive pulse applied to a step motor for driving the print head at the time the movement of the print head is commenced. This gives rise to the problem that, when a DC motor is used for driving the print head, it is impossible to start the timer circuit in timed relation to the commencement of the movement of the print head. Even if the timer circuit is started at the time a drive current is passed to the DC motor, the pitch of the dots oriented in the direction in which the characters are printed become non-uniform because the time at which the drive current is passed and the distance covered by the movement of the print head are not constant, thereby tending to degrade the printed characters.